Closed cooling water systems are important parts of power plants and other industrial systems. These systems have traditionally employed chromates for their corrosion protection. Concern about toxicity of chromates and their ecological effects had led to a consideration of the use of other anodic inhibitors such as sodium molybdates. Sodium molybdates are compatible with all the widely used biocides/polymers, scale suppressants, and sludge control agents. Therefore they are used as a part of multicompositional products (blends) along with HEDP (1-hydroxy-ethylidene-1, 1-disphonic acid), MPT (2-mercapto-benzothiazole), tolyltriazole, benzotriazole, nitrites, sodium hydroxide, pH chelants etc. to prevent corrosion of materials. See Burda, P.A., Proceedings of an International Symposium, "Surfaces, Inhibition and Passivation," The Electrochemical Society, Volume 86-7, Pages 91-103 (1986).
These molybdate-based blends are much lower in toxicity than the chromates. Some of these blends have been found to be as effective as chromates for corrosion protection of mild and cast steels, cast iron and copper alloys in deionized and nonpotable water.
However, it has been discovered in closed cooling water auxiliary systems of nuclear plants that such sodium molybdate based blends tend to produce sodium radioactive isotopes in the presence of radiation and flux of neutrons, causing contamination of cooling systems. Thus, sodium molybdate and all chemicals incorporating substantial amounts of sodium have become unsatisfactory for nuclear application.
An object of the present invention is to provide an improved closed cooling water system which can operate safely under radiation conditions.